It is well known that radiation of an appropriate wavelength falling on a P-N junction of a semiconductor body serves as a source of external energy to generate hole-electron pairs in that body. Because of the potential difference which exists at a P-N junction, holes and electrons move across the junction in opposite directions and thereby give rise to flow of an electric current that is capable of delivering power to an external circuit. Most solar cells are in the form of a silicon wafer which has been metallized, i.e., provided with metal contacts which are electrically conductive.
To provide a low cost method of generating an electrical current from the P-N junction region of the silicon wafer, it is common practice to metallize the wafer by a screen printing and firing sequence. Commercially available metallizing inks which are employed for depositing contacts on the surface of the wafer generally contain a metal powder, a finely divided glass frit, and an organic vehicle. Typical metal powders are those of silver, aluminum, nickel, gold, or copper, or alloys of these with precious metals, including platinum and palladium.
There is extensive use of Si.sub.3 N.sub.4 in solar cell technology as an anti-reflection coating, which also serves as a masking protective layer. It has good adhesion and stability when deposited on silicon. In a specific embodiment, silicon solar cells are coated with Si.sub.3 N.sub.4 on the front N-type side as an anti-reflection coating, and, in the process, the back P-type side also becomes coated with Si.sub.3 N.sub.4. In order to make electrical contact to the underlying silicon substrate, an etchant step must be employed. State of the art technology requires that the Si.sub.3 N.sub.4 be removed where contact is made, the front side etched in pattern form for application of the front side contact, and the back side similarly etched for application generally of a large area backside contact. There would be a cost savings if this etching step could be eliminated. It has now been found that aluminum-magnesium alloys can perform this function when contained in metallizing paste formulations.